<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div {
            width: 50%;
            height: 100px;
            /* 1.设置边框的粗细 */
            border-width: 3px;
            /* 2.设置边框的颜色 */
            border-color: red;
            /* 3.边框样式：实线：solid 虚线：dashed 点线：dotted */
            border-style: solid;
            /* border属于外边框 */
        }
    </style>
</head>

<body>
    <div></div>
    <!-- 修改input边框颜色 -->
    <style>
        input {
            /* 写法没有顺序 */
            border: 2px blue solid;
            /* 去除表单默认样式 */
            outline: none;
        }
    </style>
    <input type="text" name="" id="">
</body>

</html>